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An e-bike that incorporates an innovative 4-joint swinging arm initially designed by BMW engineers for its electric vehicles has been launched in Germany.
The Heisenberg XF1 e-bike, which is now entering production, uses a swinging arm that was originally developed in the early phases of research for BMW's “i” range of hybrid and electric cars.
E-bikes, sometimes known as pedelecs, are growing in popularity throughout Europe, particularly in Germany, where around 400,000 are sold each year. Several other car companies have also launched e-bikes. Last year Daimler launched an e-bike under its Mercedes Smart branding.
E-bike company HNF Heisenberg hope the improved design and performance of its XF1 will help the e-bike appeal to a younger demographic. The e-bike market is skewed towards older people because of the perception of it being “power assisted cycling”.
The drive trains of e-bikes are usually firmly attached to the main frame. The distinguishing feature of the “next generation” XF1 is that the patented swinging arm connects the rear of the e-bike to the motor, gears and carbon belt drive in its centre and allows them to float freely. This eliminates the need for a chain tensioner and enabling improved propulsion and suspension.
The kinematics are fully integrated above the mid-motor, connecting it securely to the frame. To ensure consistent spacing of the carbon drive belt between the spindle and the rear hub, the mid-motor and rear hub are integrated into the drive unit swing arm. The belt runs under tension, aligned between both toothed belt discs and is said to be able to effortlessly transfer even high peak loads from the mid-motor.
In accordance with the principle of four-joint kinematics with a virtual rotary axis around the spindle, the swinging arm is guided in such a way as to prevent the relative position of the mid-motor spindle unit from deviating in relation to the main frame.
The swing arm enables long spring travel of up to 150 mm on the rear wheel and functions without recoil from the pedal.
Compared with other rear-mounted suspension concepts, which are optimized for muscle-power, there is no stiffening of the rear swing arm when the electric motor is providing a high degree of assistance, such as during acceleration, constant travel at high speeds or on hills.
The suspension can respond sensitively at any time, ensuring excellent grip and high traction. As the amount of human driving force is relatively small, there is also no rocking movement when accelerating or breaking.